Cardio doubt

In a way to lose fat, i have a question about cardio, if i do a 45 to 1 hour in a moderate intensity, like to 65 to 75% of my heart hate, i can do it walking in a nice pace or in a bike is the best to burn fat?
Or if i make high intensity cardio, even if it minds less time like 20 to 30 minutes, like running will be more effective? i can onily do cardio in the am onily twice a week, the rest i can do it at night, just at pm, and im doing a low carb, hi pro diet